Why full size neutral single phase?

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jaggedben said:
I just want to point out that the way this OP was phrased, to me, implies somewhat unsound reasoning. The service neutral could theoretically carry as many amps as either of the ungrounded conductors if the load is somehow entirely unbalanced, i.e. all on one of those ungrounded conductors. And I don't believe there is anything special about the 1/2 number; if that number is thought to come from 120/240 that is a false understanding.

I saw a house once where some not-very-bright person put all the branch breakers on one busbar. (The panel was literally half full). Not sure why they did that, but I wouldn't tell that person that the service neutral could be smaller until they demonstrated some improved understanding in other areas. :happyno:
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Given that the OP was aware of the unbalance issue I think there was no chance he put all the breakers on one busbar. Seems to me the OP knows about trying to balance the 120 volt loads. I do agree exactly 1/2 might not happen but the OP did say "generally".

add: and you would have to ignore the 240 volt loads, which is unsound reasoning.
 
Besoeker said:
Granted that it may be improbable but, you have to concede as others have, not impossible.
So, do you take that risk?
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Yes, all the time. It is very common

And if the installation is done in the correct manor your fears of what could happen are misplaced.

Explain how your fears could be realized.
 
iwire said:
What he explained is an incorrect installation.

In a correctly planed and installed job the reduced sized neutral cannot be overloaded.
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In the scenario I described, the neutral could ebd up carrying the same current of one of the live wires.
Improbable maybe, but not impossible.
 
Besoeker said:
In the scenario I described, the neutral could ebd up carrying the same current of one of the live wires.
Improbable maybe, but not impossible.
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Are you talking about this post of yours?

Besoeker said:
What if one of the 4/0 conductors loaded to its full rated current capacity and the other not at all?
Then the neutral would have to carry all the current of the loaded 4/0 wouldn't it?
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To have that happen would require an incorrect application of the rules.

Could it happen? Sure, just like someone can always get out their tools and make any safe installation unsafe.
 
Fearing that the reduced neutral could be overloaded is similar to fearing that the 200 amp main can be overloaded because there are 400 amps of branch CBs total on each line. Possible but not probable.

VD causing light flicker might be the biggest drawback and that hasn't happened for me since CFL or LEDs, and VFDs on water pumps and AC equipment.

Add: The oversized lines with equivalent neutral I pulled surely don't count.:roll:
 
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Besoeker said:
I already did.
As did jagged bean.
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Well, not really. What jaggedben described was all the current in the ungrounded conductor matching the grounded conductor current. Pretty easy for that to happen.

To max out the grounded conductor ampacity and have that current matched in the grounded conductor as you propose is something different. To do that you have to get rid of all the 240 volt loads. Then you have to overload one side of the 120 volt circuits. Is that the kind of scenario you really want to propose? That sounds like a poster you have argued against here for making similarly outlandish statements.
 
Last month I replaced a 100 amp service cable and it was factory made with 2 #2 AL for the phase and 1 #4 AL for the neutral. They downsized it for me. :cool:

And just yesterday I ran a 60 amp feeder and I used #10 CU for the neutral.
 
peter d said:
Last month I replaced a 100 amp service cable and it was factory made with 2 #2 AL for the phase and 1 #4 AL for the neutral. They downsized it for me. :cool:

And just yesterday I ran a 60 amp feeder and I used #10 CU for the neutral.
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URD or other similar multiplexed conductor assemblies typically have neutral reduced two sizes when they have a reduced neutral. There are some with a full size neutral as well. Wire and cable manufacturers may have a wide variety of possible stock combinations, local supply houses will only have what gets higher demand in a particular area on hand at least, they may be able to order about anything that is a normal stock item from their supplier, but you may need to buy the entire reel.
 
kwired said:
URD or other similar multiplexed conductor assemblies typically have neutral reduced two sizes when they have a reduced neutral. There are some with a full size neutral as well. Wire and cable manufacturers may have a wide variety of possible stock combinations, local supply houses will only have what gets higher demand in a particular area on hand at least, they may be able to order about anything that is a normal stock item from their supplier, but you may need to buy the entire reel.
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Thanks for the lesson on supply house stock, I was not aware of that until you told me. :p
 
I never install full size neutral for service conductors. Because as mentioned earlier when the system is balanced it will not over load the neutral. Someone has to really screw up in order to over load the neutral.

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